The sterilization or removal of harmful substances is important in the agriculture and food processing field. However, many conventional methods using chemical drugs are not preferred because they could remain in foods or agricultural products. In addition, sterilization with chlorine usually results in a strong chlorine odor that is a disadvantage in this treatment.
Therefore, in the food field, ozone sterilization may be used as a sterilization method free from leaving any odor for the foods. However, this method has the disadvantage of high cost to introduce an expensive ozone gas generator in a place other than a large-scale facility.
Under such circumstances, in many industrial fields, there is a high need for development of a low cost sterilization method free from causing any harmful residual effect for human body.
Therefore, a Fenton reaction has attracted attention as a sterilization method for solving such problems.
The “Fenton reaction” refers to a reaction for generating hydroxyl radicals from hydrogen peroxide through a reaction of divalent iron. The generated hydroxyl radicals have the strongest oxidation effect among radicals.
Based on the strong oxidation effect, the reaction is expected to be applied in various fields such as sterilization and degradation of harmful substances and persistent pollutants (for example, a technology for soil cleanup by injecting a Fenton reaction catalyst into soil polluted with harmful substances).
In addition, the Fenton reaction is a technology having a low environmental burden because hydrogen peroxide is converted into harmless oxygen and water after completion of the reaction.
Hitherto, iron (II) sulfate has been generally used as a Fenton reaction catalyst. However, it is necessary to add divalent iron as needed because divalent iron is immediately oxidized to be precipitated and lose catalytic ability.
Therefore, a technology for improving solubility of ferrous sulfate using EDTA, citric acid, or the like has been developed to maintain its water solubility (see Non Patent Literature 1).
In addition, there has been reported a technology for sterilizing a mold based on the strong oxidation effect of the Fenton reaction (see Patent Literature 1).
However, in such conventional methods, there is a fatal problem in that divalent iron used as a catalyst is very unstable and cannot be prevented from being oxidized into trivalent iron, resulting in losing the catalytic ability in a short time.
Therefore, there has been required development of a stable Fenton reaction catalyst that can maintain the state of divalent iron, which is in nature unstable, for a long period of time.
Further, in the conventional Fenton reaction catalysts, trivalent iron or metallic iron, which is present in large amounts in the nature and can be inexpensively supplied, cannot be used as an iron raw material.